Add knock information in admin exported data (#11171)

Signed-off-by: Rafael Goncalves <rafaelgoncalves@riseup.net>

synapse/handlers/admin.py

@@ -90,6 +90,7 @@ class AdminHandler:
                 Membership.LEAVE,
                 Membership.BAN,
                 Membership.INVITE,
+                Membership.KNOCK,
             ),
         )
 
@@ -122,6 +123,13 @@ class AdminHandler:
                         invited_state = invite.unsigned["invite_room_state"]
                         writer.write_invite(room_id, invite, invited_state)
 
+                if room.membership == Membership.KNOCK:
+                    event_id = room.event_id
+                    knock = await self.store.get_event(event_id, allow_none=True)
+                    if knock:
+                        knock_state = knock.unsigned["knock_room_state"]
+                        writer.write_knock(room_id, knock, knock_state)
+
                 continue
 
             # We only want to bother fetching events up to the last time they
@@ -238,6 +246,20 @@ class ExfiltrationWriter(metaclass=abc.ABCMeta):
         """
         raise NotImplementedError()
 
+    @abc.abstractmethod
+    def write_knock(
+        self, room_id: str, event: EventBase, state: StateMap[dict]
+    ) -> None:
+        """Write a knock for the room, with associated knock state.
+
+        Args:
+            room_id: The room ID the knock is for.
+            event: The knock event.
+            state: A subset of the state at the knock, with a subset of the
+                event keys (type, state_key content and sender).
+        """
+        raise NotImplementedError()
+
     @abc.abstractmethod
     def finished(self) -> Any:
         """Called when all data has successfully been exported and written.